R Shiny styleColorBar applied to a subset of columns

Question

I have a datatable inside an R shiny app and I'm trying to do what is illustrated in the following manual: https://rstudio.github.io/DT/010-style.html -> Style a full table. However, I'm trying to customize the colors of only columns 2 and 3 in this example.

My code is the following:

datatable(df, 
                  filter = 'none',
                  rownames= FALSE,
                  caption = paste0("Execution Alpha by sector."),
                  options = list(scrollX = F
                                 #,dom = 'ft'
                                 , lengthChange = T
                                 , pagingType = "numbers"  # this hides the Next and Previous buttons -->  https://datatables.net/reference/option/pagingType
                                 , autoWidth = T
                                 ,pageLength = 20 # this determines how many rows we want to see per page
                                 , info = FALSE #  this will hide the "Showing 1 of 2..." at the bottom of the table -->  https://stackoverflow.com/questions/51730816/remove-showing-1-to-n-of-n-entries-shiny-dt
                                 ,searching = FALSE  # this removes the search box  ->  https://stackoverflow.com/questions/35624413/remove-search-option-but-leave-search-columns-option
                  ))  %>%
                      formatStyle(                            
                        colnames(df)[2:3],
                        background = styleColorBar(df[,2:3], 'lightblue'),
                        backgroundSize = '100% 80%',
                        backgroundRepeat = 'no-repeat',
                        backgroundPosition = 'left' # center
                      )

I get an error saying: "only defined on a data frame with all numeric variables" however all the values in columns 2 and 3 are numbers. Any suggestions? Thanks